Mowers of the riding type are previously known. Such machines can be provided with front mounted cutting attachments and cutting attachments which are centrally placed between the front- and rearwheels respectively.
The engine can be placed in front of or behind the driver and further there are front wheel- and rearwheel steering and driving. Each type has its own advantages and drawbacks. For instance mowers with centrally placed cutting attachments generally have the drawback that the front wheel presses down the grass before it reaches the cutting attachment which means that parts of a lawn are badly cut. A mower having a front mounted cutting attachment, rear mounted engine and rear wheel steering gives a good survey of the cutting attachment and the surface to be cut whereas the drawback is a large turning radius since the steering angle is limited with the respect to the friction between the lawn and the steering wheels. A rear wheel driven machine with the engine at the rear, centrally placed cutting attachment and with front wheel steering gives advantages with respect to the transmission because of the short distance between the engine and driving wheels and cutting attachment respectively but gives an even large turning radius since the centrally placed cutting attachment creates a larges wheel basis then machines having front mounted attachments. In order to shorten the time during shunting in connection with turnings it is desirable that a machine has as short turning radius as possible.
In a type of machine which is a rather good compromise between different wishes the chassis comprises two sections which are pivotally connected to each other half way between the front and rear wheels. The front section of the chassis supports the two front wheels which are mounted on separate shafts, the cutting attachment which is placed ahead of the front wheels and the operator. The rear section supports engine with gear box, differential gearing and rear shaft, the steering being effected by turning the rear section with respect to the front section about a vertical steering axis. The pivot point is in this machine so designed that turning the rear section with respect to the front section also can be effected about a swinging axis which is directed in the travelling direction of the mower and horizontally placed on the front section in order to make it possible for the wheels to follow irregularities on the ground.
Even if the machine described above in most respects has rather good characteristics, its turning radius is after all limited to something which corresponds to about 45.degree. turn of angle of the rear section. This depends on that the rear wheels--with the reasonable length of the machine--when being further turned would get in touch with the front wheels and that further turning of the wheels would lead to too large variation in the ground pressure between the two driving wheels because of the position of the swinging axis. At a certain steering angle the ground pressure on the inner wheel becomes so small that driving ceases. The ground pressure of this wheel can even become negative that is the wheel is lifted from ground which causes the risk for tipping. Moreover the cutting attachment of this machine cannot be driven directly by one single belt from the engine since the distance between engine and cutting attachment changes with the steering angle. Further drawbacks are that there is a demand for operating devices on the engine following its movement and that a certain undesirable selfguiding is achieved because the grass during cutting brakes the knives which causes a moment between the two sections of the machine.